1. Field of the Invention
The present invention generally relates to an isolated power conversion system, and more specifically to an isolated power conversion system provided with at least one digital PWM controller at the primary and/or the secondary side performing a preset power control function based on actual application, receiving/transmitting a digital signal like a detected voltage or current of the secondary side back to the primary side so as to control the switching transistor at the primary side, or inverting the PWM signal to generate and transmit an inverted PWM signal to the secondary side to synchronously control the switching transistor, thereby enhancing stability of power conversion and greatly improving quality of electrical signal.
2. The Prior Arts
Various electronic products need specific power with different voltage or current to correctly operate. For example, general integrated circuits (ICs) need 5V or 3V, electric motors require 12V DC power, but for lamps of LCD monitors, much higher voltage like 115V is just sufficient. Thus, it is greatly needed for suitable power converters to meet the requirements of actual applications, and technology of power conversion has been developed and becomes an essential part of the electronic industry.
In general, technology of power conversion is roughly classified by two types: isolated and non-isolated. The isolated power conversion separates the input power and the load to prevent the loading device from damage due to abnormal surge current resulted from the input power. Therefore, the isolated power conversion is substantially safer and the circuit design is simpler. In contrast, the non-isolated power conversion induces more concerns and usually needs to meet more severe regulation for the sake of safety.
Refer to FIG. 1 illustrating the isolated power conversion system in the prior arts. An AC power is rectified, filtered and then transmitted to a primary coil of a transformer TR. A drain of a driving switching transistor Q1 is connected to the primary coil, and a source of the transistor Q1 is connected to a sensing resistor to generate a sensing signal. In addition, an induction voltage is generated by a secondary coil of the transformer TR due to induction of a current flowing through the primary coil, and transmitted to an output unit for further filtration and rectification. The output unit then generates an output power Vo to supply an external load.
In particular, a PWM (pulse width modulation) controller U1 generates a PWM driving signal to control a gate of the transistor Q1, thereby controlling the operation of turning on/off the transistor Q1. Further, a photocoupler is connected to the output unit, generates and transmits a feedback signal to the PWM controller U1 so as to achieve isolation for power conversion.
Further refer to FIG. 2 illustrating another isolated power conversion system in the prior arts. The isolated power conversion system in FIG. 2 is similar to the system in FIG. 1, and the photocoupler U2 is also used to generate the feedback signal for the PWM controller U1. However, one difference is that a constant-voltage-constant-current controller U3 is employed to control the load consisting of LEDs connected in series for a feature of constant voltage and constant current so as to maintain light quality and prolong lifetime of the LEDs.
Obviously, one drawback of the above isolated power conversion system in the prior arts is that the feedback signal generated by the photocoupler U2 is an analog signal and easily interfered by external electrical noise such that noise margin is poor. Stability of overall electrical operation is adversely affected.
Therefore, it is greatly needed to provide a new isolated power conversion system employing a signal blocking unit as a connection interface between a first PWM controller and a second PWM controller to implement digital communication so as to enhance ability of resisting noise, improve stability of electrical operation, avoid malfunction and secure signal quality, thereby overcoming the above problems in the prior arts.